Method and system for lithium isotope separation

Abstract

A method and system for isotopicly separating lithium-6 and lithium-7 from a mixture thereof. The method comprises the step of efficiently separating the isotopes using molecular distillation having a heat exchange array supplied by a nuclear reactor (1). The system comprises a combination of a molecular distillation apparatus having a distiller (20) and a nuclear reactor (1) having a heat exchange array to provide the heat required for the process.

Description

Technology Field

[0001] The present disclosure relates to a method and system for the separation of lithium isotopes of lithium-7 and lithium-6, specifically the separation of lithium-7 and lithium-6 isotopes from naturally occurring lithium. Background Technology

[0002] Naturally occurring lithium is a mixture of varying proportions of lithium-7 and lithium-6 resulting from the geological separation of the two isotopes, with the concentration of lithium-6 varying between approximately 2% and 8%, and 5% being the standard.

[0003] Molten salt reactors utilizing lithium fluoride or chloride salts require substantially enriched lithium-7 because the thermal capture neutron cross sections of lithium-6 and lithium-7 for thermal neutrons differ significantly, being 941 barn and 0.014 barn, respectively, and in order to minimize the generation of tritium from neutron capture by lithium-6.

[0004] Naturally occurring lithium has a thermal capture cross-section of approximately 65 barn, which is very high compared to, for example, naturally occurring sodium, with a thermal capture cross-section of 0.5 barn, or naturally occurring potassium, with a thermal capture cross-section of 2 barn. For comparison, 99.9% enriched lithium-7 (3N 7Li) has a thermal capture cross-section of 0.95 barn, 99.99% enriched lithium-7 (4N 7Li) has a thermal capture cross-section of 0.11 barn, and 99.999% enriched lithium-7 (5N 7Li) has a thermal capture cross-section of 0.02 barn. This means that 99.99% to 99.999% enriched lithium-7 (4-5N 7Li) is preferred for using the lithium in molten salt reactor salts.

[0005] Examples of lithium fluoride salts that can be used in molten salt reactor salts include 7LiF-BeF2, 7LiF-BeF2-UF4, 7LiF-ThF4, 7LiF-ThF4-UF4, and 7LiF-ThF4-PuF3. Examples of lithium chloride salts that can be used in molten salt fast reactors include 7LiCl-KCl-UCl3, 7LiCl-UCl3, 7LiCl-PuCl3, and 7LiCl-UCl3-PuCl3.

[0006] Highly enriched Lithium-7 is particularly important for thermal molten salt breeder reactors, which have the potential to scale up much faster than other nuclear technologies in situations where the supply of fissile fuel is limited. To meet global energy demand, tens of thousands of tons of Lithium-7 enrichment capacity will be required annually over the next few decades to scale up thermal molten salt breeder reactors, which is a major challenge in scaling up this type of reactor.

[0007] When lithium-6 captures thermal neutrons, there is a high probability that tritium will be produced. The production of tritium from the lithium-6 is considered a risk of radionuclide emission in nuclear reactors, but it is also a target in some fusion reactor blankets. Therefore, while nuclear (fission) reactors utilizing lithium require enriched lithium-7, fusion reactors require enriched lithium-6, and the separation of lithium isotopes can create synergy for both industries.

[0008] Examples of fluoride salts that can be used as fusion reactor blanket salts include 6LiF-BeF2 and 6LiF-7LiF-BeF2, where the beryllium also acts as a neutron multiplier, and examples of molten metal alloys that can be used in fusion reactor blankets include Li, Li-Pb, and Li-Bi.

[0009] The primary method for industrialized lithium isotope separation is the COLEX process, which is a two-liquid-phase chemical exchange between an aqueous lithium hydroxide solution and a mercury-lithium amalgam, where lithium-6 has a slightly greater affinity for the mercury amalgam. The COLEX process involves large amounts of mercury and mercury compounds, which, along with high energy consumption, makes the process unattractive for future lithium isotope separation.

[0010] The COLEX process described above is a mercury-based chemical approach for the isotopic separation of lithium-6 and lithium-7, utilizing the fact that lithium-7 has a greater affinity for the mercury element than lithium-6 by contacting aqueous lithium hydroxide (LiOH) with a lithium-mercury amalgam. The COLEX separation process involves a counter-flow method in which aqueous lithium hydroxide flows upward and the lithium-mercury amalgam flows downward through a series of exchange columns containing cation exchange resins. Mercury preferentially discharges the lithium-6 fraction, while lithium-7 flows mainly with the hydroxide. The amalgam is separated from the lithium (enriched with lithium-6) at the bottom of the column, and the mercury is recovered for subsequent use. The lithium-7 fraction is electrolyzed to discharge a lithium hydroxide solution at the top. The operating temperature, flow rate, and column length all affect the degree of enrichment achievable through this process.

[0011] The facility using the aforementioned COLEX process, located in Oak Ridge, Tennessee, operated between 1955 and 1963 and produced the current U.S. 6 Li and 7 Li stockpiles.

[0012] The above COLEX process has several disadvantages, such as the following:

[0013] - Toxicity caused by the accompanying large amount of mercury.

[0014] - The tendency of amalgam to decompose in aqueous solution.

[0015] - Formation of dangerous mercury-containing waste

[0016] - High energy consumption.

[0017] - Potentially catastrophic environmental impact due to the requirement of significant amounts of mercury (24 million pounds used in the United States between 1955 and 1963) and the high possibility of leakage into the environment.

[0018] Many methods for isotope separation of the lithium have been studied and developed, including 2-liquid-phase chemical exchange, ion exchange resins, ion exchange membranes, laser absorption, thermal diffusion, electrophoresis, fractional crystallization, microalgae, and molecular distillation. While many of these methods have been shown to work, there is not yet a method that can economically replace the COLEX process.

[0019] Research on the separation of lithium metal isotopes using molecular distillation was limited and was eventually abandoned after only a few papers were published in the late 1950s and early 1960s, one of the reasons being the high energy and high temperature requirements of the process.

[0020] CN115193253 discloses a method and device for separating 6Li and 7Li isotopes using molecular distillation. Based on the difference in atomic mass between 6Li and 7Li, 6Li and 7Li are separated via thermal evaporation. This method is characterized by the fact that, after heating and evaporating natural metallic lithium within a vacuum chamber and maintaining the lithium vapor under a constant pressure to achieve thermal equilibrium, 6Li is mainly distributed in the upper part of the vacuum chamber and 7Li is mainly distributed in the lower part of the vacuum chamber. The boundary between the 6Li and 7Li vapors can be determined by the content ratio of 6Li and 7Li in the natural metallic lithium, temperature, and pressure. A partition plate, which can be inserted or removed at any time as needed, is placed at the boundary between the 6Li and 7Li vapors. During thermal equilibrium, when the partition plate is inserted, 6Li and 7Li vapors f < n > are released into their respective cooling vessels and cooled into a solid, and a protective layer is added to realize the separation of 6Li and 7Li.

[0021] The objective is to provide a lithium isotope separation method and system that overcomes or at least reduces the aforementioned problems.

[0022] The above objectives and other objectives are achieved by the composition of the independent claims. Additional forms of implementation are apparent from the dependent claims, specification, and drawings.

[0023] Since lithium metal melts at 180 °C and boils at 1330 °C, simple distillation does not seem attractive due to the high boiling point of the molten lithium and the low separation factor at high temperatures. However, the inventors realized that even at temperatures much lower than the boiling point of lithium, a separation factor sufficient to enable efficient isotope separation is secured due to the large molecular weight difference between molten lithium-6 and lithium-7. The molecular weight difference between lithium-6 and lithium-7 is sufficient to achieve a theoretical separation factor of 1.08, while the difference in vapor pressure is negligible.

[0024] For efficient molecular distillation, the mean free path length of the vapor atoms or molecules must be similar to or longer than the distance between the evaporation and condensation surfaces. The mean free path length of the lithium atoms depends on the vacuum level and lithium vapor pressure of the distiller, which in turn depends on the temperature of the lithium. The mean free path length of the lithium vapor is approximately 50 mm at 400°C, 20 mm at 500°C, and 15 mm at 550°C. Since the free path length increases with lower temperatures, it is generally more effective to perform the molecular distillation at low temperatures, but the distillation rate is also lowered in accordance with the lower evaporation rate. Therefore, it is necessary to find a balance between efficient distillation and distillation rate for a specific distiller. The inventors have determined that for lithium molecular distillation, it is optimal to set the evaporation surface temperature to approximately 500-600°C and the low-temperature side temperature to approximately 100°C lower, i.e., approximately 400-500°C.

[0025] The inventors have reached the insight that liquid-phase short-distance molecular distillation of lithium is attractive because it allows for multiple stages with very short distances between evaporation and condensation surfaces. Furthermore, the inventors have reached the insight that since molten lithium is compatible with ordinary stainless steel, the distiller can be manufactured using commonly available materials and manufacturing methods. However, these types of distillers consume a large amount of energy because they must simultaneously cool the top of the distiller and heat the bottom of the distiller at each stage.

[0026] According to the first aspect, a method for isotopicly separating lithium-6 and lithium-7 from a mixture is provided, said method comprising:

[0027] - A step of isotopicly separating a feed stream of a molten lithium metal feed material containing a mixture of lithium-6 and lithium-7 into a concentrated molten lithium-6 stream and a concentrated molten lithium-7 stream through molecular distillation of the feed stream of the molten lithium metal feed material using a still or a series of stills,

[0028] - A step of heating a heat exchange medium to a temperature of at least 400°C in a nuclear reactor, and

[0029] - A step of supplying the heated heat exchange medium to the molecular distillation apparatus.

[0030] By supplying heat to the molecular distillation process using a nuclear reactor, the nuclear distillation process, which is inherently very energy-intensive, utilizes readily available and relatively inexpensive high-temperature heat from the nuclear reactor, thereby reducing costs; consequently, the cost of molecular distillation is substantially reduced, making molecular distillation economically competitive with other known lithium isotope separation methods.

[0031] According to a possible embodiment of the first aspect above, the nuclear reactor is one of the following:

[0032] - Gas-cooled reactor, preferably a high-temperature gas-cooled reactor (HTGR) or a very-high-temperature reactor (VHTR),

[0033] - Liquid metal cooled reactor (LMR),

[0034] - Heat pipe cooled reactor (HPR),

[0035] - Molten salt reactor (MSR).

[0036] According to a possible embodiment of the first aspect above, an evaporator is operably connected to the distiller and includes the step of supplying the heated heat exchange medium to the evaporator.

[0037] According to a possible embodiment of the first aspect above, the nuclear reactor comprises a reactor core, a primary heat exchange loop including a primary heat exchange medium, the primary heat exchange loop passing through the reactor core and passing through a primary heat exchanger, and a secondary heat exchange loop including a secondary heat exchange medium, wherein the secondary heat exchange loop passes through the primary heat exchanger and transfers heat from the reactor core to the secondary heat exchange medium by circulating the primary heat exchange medium in the primary heat exchange loop and by circulating the secondary heat exchange medium in the secondary heat exchange loop.

[0038] According to a possible implementation form of the first aspect above, the secondary heat exchange loop passes through the evaporator.

[0039] According to a possible embodiment of the first aspect above, the distiller comprises one or more of the following:

[0040] - Vertical column distiller,

[0041] - Horizontal still,

[0042] - A vacuum port for connecting to a vacuum system to form a high or ultra-high vacuum,

[0043] - Feed port for supplying a mixture of molten lithium,

[0044] - Reflux port,

[0045] - First upper outlet port for concentrated vapor lithium-6,

[0046] - Second lower outlet port for concentrated molten lithium-7,

[0047] - Trace heating elements

[0048] - Insulation material.

[0049] According to a possible embodiment of the first aspect above, the evaporator is operably connected to the distiller, and the heat exchange medium supplying heat to the evaporator comprises a molten salt, preferably a nitrate, fluoride, or chloride salt having a suitable melting and boiling point.

[0050] According to a possible embodiment of the first aspect above, a condenser is operably coupled to the distiller and includes the step of removing heat from the condenser with a heat exchange medium, preferably a molten salt, preferably a nitrate, fluoride, or chloride salt.

[0051] According to a possible embodiment of the first aspect above, the heat exchange medium is circulated in a loop comprising one or more intermediate heat exchangers located between the evaporator and the condenser and includes the step of increasing the temperature drop between the evaporator and the condenser, wherein the one or more intermediate heat exchangers preferably include a counterflow recuperator.

[0052] According to a possible embodiment of the first aspect above, the heat exchange medium comprises a NaNO3-KNO3 eutectic salt having a melting point of approximately 250°C, and includes the step of heating the evaporator to at least approximately 400°C, preferably approximately 550°C, and the maximum operating temperature is 560°C because the NaNO3-KNO3 eutectic salt undergoes thermal decomposition at high temperatures.

[0053] According to a possible embodiment of the first aspect above, the method includes the step of cooling the condenser to approximately 300°C, preferably to approximately 260°C.

[0054] According to a possible embodiment of the first aspect above, the method comprises the steps of heating the evaporator to approximately 400°C, preferably approximately 550°C, using a LiNO3-NaNO3-KNO3 eutectic salt having a melting point of approximately 120°C, and cooling the condenser to approximately 150°C, wherein the maximum operating temperature of the LiNO3-NaNO3-KNO3 eutectic salt is 560°C due to thermal decomposition.

[0055] According to a possible embodiment of the first aspect above, the method comprises using a LiF-NaF-KF eutectic salt having a melting point of approximately 450°C, which includes the step of heating the evaporator to approximately 600°C and cooling the condenser to approximately 500°C using a LiF-NaF-KF salt or a LiNO3-NaNO3-KNO3 eutectic salt, wherein the LiF-NaF-KF eutectic salt is preferably operated at a maximum operating temperature of 700°C to prevent excessive corrosion of the salt-containing material.

[0056] According to a possible embodiment of the first aspect above, the method comprises the steps of heating the evaporator using a LiF-NaF-KF or NaNO3-KNO3 salt and cooling the condenser using an organic refrigerant.

[0057] According to a possible embodiment of the first aspect above, the still comprises packing, preferably structured packing, and / or the still is a vertical still.

[0058] According to a second aspect, a system for isotopicly separating lithium-6 and lithium-7 from a mixture is provided, said system comprising:

[0059] - Molecular distillation apparatus including the following:

[0060] At least one distiller configured to isotopicly separate a feed stream of molten lithium metal feed material containing a mixture of lithium-6 and lithium-7 into a concentrated molten lithium-6 stream and a concentrated molten lithium-7 stream,

[0061] An evaporator operably coupled to the above-mentioned at least one distiller,

[0062] - Nuclear reactor including a reactor core,

[0063] The above system includes a heat exchange array for transferring heat from the nuclear reactor core to the evaporator using at least one heat exchange medium, and the heat exchange array is configured to supply heat to the evaporator with a heat exchange medium having a temperature of at least 400°C.

[0064] According to a possible embodiment of the second aspect above, the nuclear reactor comprises the following:

[0065] A primary heat exchange loop comprising a primary heat exchange medium, wherein the primary heat exchange loop passes through the reactor core and passes through the primary heat exchanger, and

[0066] A secondary heat exchange loop comprising a secondary heat exchange medium, wherein the secondary heat exchange loop passes through the primary heat exchanger.

[0067] According to a possible embodiment of the second aspect above, the distiller comprises one or more of the following:

[0068] - Vertical column distiller,

[0069] - Horizontal still,

[0070] - A vacuum port for connecting to a vacuum system to form a high or ultra-high vacuum,

[0071] - Feed port for supplying molten lithium mixture,

[0072] - Reflux port,

[0073] - First upper outlet port for concentrated vapor lithium-6,

[0074] - Second lower outlet port for concentrated molten lithium-7,

[0075] - Trace heating element,

[0076] - Insulation material.

[0077] According to a third aspect, a method for isotopicly separating lithium-6 and lithium-7 from a mixture is provided, said method comprising:

[0078] - A step of isotopicly separating a molten lithium metal material containing a mixture of lithium-6 and lithium-7 into concentrated molten lithium-6 and concentrated molten lithium-7 through molecular distillation of the molten lithium metal material using a molecular distillation apparatus including a distiller or a series of distillers,

[0079] - A step of heating a heat exchange medium to a temperature of at least 400°C in a nuclear reactor, and

[0080] - A step of supplying the heated heat exchange medium to the molecular distillation apparatus to drive the molecular distillation process.

[0081] According to a second aspect, a system for isotopicly separating lithium-6 and lithium-7 from a mixture is provided, said system comprising:

[0082] - Molecular distillation apparatus including the following:

[0083] At least one distiller configured to isotopicly separate a molten lithium metal material containing a mixture of lithium-6 and lithium-7 into concentrated molten lithium-6 and concentrated molten lithium-7,

[0084] An evaporator operably coupled to the above-mentioned at least one distiller,

[0085] - Nuclear reactor including a reactor core,

[0086] The above system includes a heat exchange array for transferring heat from the nuclear reactor core to the evaporator using at least one heat exchange medium, and the heat exchange array is configured to supply heat to the evaporator with a heat exchange medium having a temperature of at least 400°C.

[0087] These points and other aspects will become apparent from the embodiments and implementations described below. Brief explanation of the drawing

[0088] In the following detailed description of the disclosure, the aspects, embodiments, and forms of the invention will be described in more detail with reference to the exemplary embodiments shown in the drawings, wherein: FIG. 1 is a schematic diagram of a system according to one embodiment including a molecular distillation apparatus and a nuclear reactor, and FIG. 2 is a schematic diagram of a system according to another embodiment including a molecular distillation apparatus and a nuclear reactor, and FIG. 3 is a schematic diagram of another system according to another embodiment including a molecular distillation apparatus and a nuclear reactor. Specific details for implementing the invention

[0089] FIG. 1 shows one embodiment of a system for isotopicly separating lithium-6 and lithium-7 from a mixture through molecular distillation. The system comprises a molecular distillation apparatus and a nuclear reactor (1). The molecular distillation apparatus comprises at least one distiller (20) configured to isotopicly separate a feed stream of molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into a concentrated molten lithium-6 stream and a concentrated molten lithium-7 stream. The molecular distillation apparatus may comprise several distillers (20) connected in series. In the embodiment shown in FIG. 1, the distiller (20) comprises a vertical column (22), a vacuum port (29) for connecting to a vacuum system (40) for forming a high or ultra-high vacuum, a feed port (24) for receiving the mixture of the molten lithium, a reflux port (26), a first upper outlet port (27) for concentrated vapor lithium-6, a second lower outlet port (28) for concentrated molten lithium-7, a structured filler (23), a trace heating element (31), and an insulating material (32). However, it should be understood that this is merely an example of a distiller (20) that can be used in the distillation apparatus, and that other types of distillers, such as a horizontal distiller (not shown), may also be used. The molten lithium metal feed material, comprising the mixture of lithium-6 and lithium-7, is supplied to the vertical column (22) through a feed conduit leading to the feed port (24), preferably supplied in a substantially constant stream, but may also be supplied in an intermittent stream. The vacuum port (29) is connected to a vacuum pump (4) that creates a high or ultra-high vacuum inside the vertical column (22). The evaporator (25) is operably connected to two separate locations of the distiller (20) through an evaporator conduit (29) having an inlet at the lowest region of the vertical column (22) and an outlet slightly above the lowest region of the vertical column (22).In this embodiment, the inlet of the evaporator conduit (29) is connected to the second lower outlet (28), but it should be understood that the evaporator (29) may have its own port connected to the lowest region of the vertical distillation column (22). The concentrated molten lithium-7 is circulated through the evaporator conduit (29) and the evaporator (25) by a circulation pump (not shown) or other device capable of forcing the circulation of the molten lithium-7.

[0090] The above-mentioned packing material (23), preferably a structured packing material (23), provides a large surface area for the counter-flow of molten lithium metal and lithium metal vapor. The structured packing material (23) is preferably optimized for short-distance molecular distillation of lithium by taking into account the operating temperature of the distiller (20) in the design of the structured packing material (23). A relatively long packing column (23) serves as a plurality of theoretical stages allowing a large separation factor in one or more packing columns (23). The distillation process is carried out above the melting point of molten lithium, but preferably below the boiling point of molten lithium.

[0091] The first upper outlet (27) is connected to the inlet of the condenser (30), and the outlet of the condenser (30) is branched into a reflux (26) and an off-stream (21) of concentrated molten lithium-6.

[0092] The condenser (30) is operably coupled to the distiller (20) to remove heat from the concentrated vapor lithium-6 stream coming from the upper outlet (27), thereby at least partially condensing the concentrated vapor lithium-6 stream coming from the upper outlet (27) in the condenser (30). The condenser (30) is cooled by a heat exchange medium to remove heat from the condenser (30). In one embodiment, the heat exchange medium is a molten salt, preferably a nitrate, fluoride, or chloride salt.

[0093] The above system includes a heat exchange array for transferring heat from the nuclear reactor (1) to the evaporator (25) using at least one heat exchange medium, and the heat exchange array is configured to supply heat to the evaporator (25) with a heat exchange medium having a temperature of at least 400°C supplied to the heat exchange array.

[0094] The above nuclear reactor (1) comprises a reactor core (2) and a primary heat exchange loop (3) containing a primary heat exchange medium, and the primary heat exchange loop (3) passes through the reactor core (2) and passes through a primary heat exchanger (4). The primary heat exchange loop (3) includes a primary circulation pump (5) for circulating the primary heat exchange medium in the primary heat exchange loop (3).

[0095] The above system includes a secondary heat exchange loop (1) comprising a secondary heat exchange medium, and the secondary heat exchange loop (12) passes through the primary heat exchanger (4) and the evaporator (25) to transfer heat from the nuclear reactor (1) to the evaporator (25). A circulation pump (not shown) may be provided in the secondary heat exchange loop (12).

[0096] To supply the heat required for the above molecular distillation process, the secondary heat exchange medium is heated to a temperature of approximately 400°C or higher using the nuclear reactor (1).

[0097] The nuclear reactor (1) may be a gas-cooled reactor, such as a high-temperature gas-cooled reactor (HTGR) or a very high-temperature reactor (VHTR), a liquid metal-cooled reactor (LMR), a heat pipe-cooled reactor (HPR), or a molten salt reactor (MSR). For this reason, the first heat exchange medium may be gas, liquid metal, or molten salt, and the second heat exchange medium may be gas, liquid metal, or molten salt, and any combination of materials used for the first and second heat exchange media is possible.

[0098] For this reason, the heated secondary heat exchange medium is supplied to the molecular distillation device, where it is used to drive the isotope separation process in the evaporator (25).

[0099] The secondary heat exchange medium utilized in the evaporator (25) comprises a molten salt having a suitable melting and boiling point, such as a NaNO3-KNO3 eutectic salt having a melting point of approximately 250°C, or this is one embodiment. The evaporator (25) is heated to at least approximately 400°C, preferably approximately 550°C.

[0100] The secondary heat exchange medium used in the above evaporator (25) comprises a LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°C, or this is another embodiment.

[0101] The secondary heat exchange medium used in the evaporator (25) comprises a LiF-NaF-KF eutectic salt with a melting point of approximately 450°C to heat the evaporator to approximately 600°C, preferably approximately 700°C, or this is still another embodiment.

[0102] FIG. 2 shows another embodiment of a system for isotopicly separating lithium-6 and lithium-7 from a mixture through molecular distillation. In this embodiment, structures and features identical or similar to those previously described or shown herein are denoted by the same reference numbers used previously for brevity. This embodiment is essentially identical to the first embodiment except that the secondary heat exchange loop (12) passes through both the evaporator (25) and the condenser (30). For this reason, the configuration and elements of the same system and their functions are not described again, and instead, the embodiment is referenced.

[0103] To increase the temperature drop between the evaporator (25) and the condenser (30), at least one intermediate heat exchanger (50) is positioned between the evaporator (25) and the condenser (30). The at least one intermediate heat exchanger (50) preferably includes a countercurrent recovery unit. The heat removed from the intermediate heat exchanger (50) / countercurrent recovery unit may be used for other purposes, for example, power generation or district heating. Another heat exchanger (52) may be positioned downstream of the condenser (30). The heat removed from the other heat exchanger (52) may be used, for example, for power generation or district heating.

[0104] The heat exchange medium for cooling the condenser (30) may be a molten salt, such as a LiNO3-NaNO3-KNO3 eutectic salt with a melting point of approximately 120°C, which allows the condenser to be cooled to approximately 150°C, preferably approximately 130°C.

[0105] Alternatively, the evaporator can be heated to approximately 600°C, preferably approximately 700°C, using a LiF-NaF-KF eutectic salt having a melting point of about 450°C, and the condenser can be cooled to approximately 550°C, preferably approximately 400°C, using the LiF-NaF-KF salt or the LiNO3-NaNO3-KNO3 eutectic salt.

[0106] In some embodiments, an organic coolant may be used to cool the condenser (30) while maintaining the high temperature required for isotope separation.

[0107] FIG. 3 shows another embodiment of a system for isotopicly separating lithium-6 and lithium-7 from a mixture through molecular distillation. In this embodiment, structures and features identical or similar to those previously described or shown herein are denoted by the same reference numbers used previously for brevity. This embodiment is essentially identical to the first embodiment except that the secondary heat exchange loop (12) passes through a multi-stage horizontal distiller (62). For this reason, the configuration and elements of the same system and their functions are not described again, and instead, the embodiment is referenced.

[0108] In the secondary heat exchange loop (12), the heat exchange medium is heated to a high temperature by exchanging heat with the heat exchange medium in the primary heat exchange loop (3) in the primary heat exchanger (4). The high-temperature heat exchange medium in the secondary heat exchange loop (12) leaving the primary heat exchanger (4) is supplied to a lower passage extending along the lower horizontal side of the horizontal distiller (62) to heat the molten lithium in the lower part of the horizontal distiller (62), and there the heat exchange medium passes through a heat exchanger (54), where it exchanges heat with a cooling medium to lower the temperature of the heat exchange medium entering the upper part of the horizontal distiller (62). From the heat exchanger (54), the heat exchange medium is supplied to an upper passage extending along the upper horizontal side of the horizontal distiller column (62) where the condensation element (130) is located, and there the heat exchange medium is supplied back to the primary heat exchanger (4). The molten lithium metal feed material, comprising the mixture of lithium-6 and lithium-7, is supplied to the horizontal distiller (62) through a feed conduit leading to the feed port (24) in the lower part of the horizontal distiller (62), preferably supplied as a substantially constant stream, but may also be supplied as an intermittent stream. The horizontal distiller comprises a plurality of horizontally distributed stages (shown as, for example, three in this embodiment), but typically the distiller consists of 100 or more stages. Each distiller may include one or more trays, which in turn may include a plurality of stages. In the case of a plurality of trays, it is preferable that they be connected to each other to provide constant concentration performance. Molten lithium flows from one stage to the next through the bottom of each tray. The bottom of the tray is heated, while the top is cooled, so that the lithium metal evaporates across the bottom of the tray and condenses at the top of the tray. The trays are configured so that the lithium flow from one stage to another is in series.As the lithium passes through the bottom of one stage, some of the lithium evaporates and condenses on the lid of the stage forming a condensation element (130), which is inclined so that the condensed lithium metal falls to the bottom of the previous stage. This moves the condensed lithium backward toward the first stage, while the condensed lithium falling to the bottom of the stage displaces the molten lithium forward, and potentially the bottom of the tray is inclined to move the molten lithium forward. In this way, a countercurrent stream of lithium is provided, where the lithium-6-rich condensed lithium flows backward through the stage toward the first outlet port (67), and the remaining lithium-7-rich lithium flows forward through the stages toward the second outlet port (68). In this way, the concentrated lithium-6 is concentrated at the beginning of the tray and the concentrated lithium-7 is concentrated at the end of the tray.

[0109] The various aspects and forms of implementation described above have been described together with various embodiments of the present invention. However, those skilled in the art can understand and implement other variations of the disclosed embodiments in carrying out the claimed object by studying the drawings, the present disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude the plural.

[0110] References used in the claims should not be interpreted as limiting the scope. Unless otherwise stated, the drawings should be read in conjunction with the specification (e.g., cross-hatching, arrangement of parts, proportions, degrees, etc.) and should be considered part of the entire written description of the disclosure. The terms “horizontal,” “vertical,” “left,” “right,” “up,” and “down” as used herein, as well as their adjectives and adverbial derivatives, simply refer to the orientation of the depicted structure when a particular drawing is oriented toward a reader of this disclosure. Likewise, the terms “inwardly” and “outwardly” generally refer, where appropriate, to the orientation of a surface relative to an axis of extension or rotation of the surface.

Claims

Claim 1 A method for isotopically separating lithium-6 and lithium-7 from a mixture of lithium-6 and lithium-7, the method comprising: - isotopicly separating a feed stream of a molten lithium metal feed material containing the mixture of lithium-6 and lithium-7 into a concentrated molten lithium-6 stream and a concentrated molten lithium-7 stream through molecular distillation of the feed stream of the molten lithium metal feed material using a still (20) or a molecular distillation apparatus comprising a series of stills (20); the method further comprising: - heating a heat exchange medium to a temperature of at least 400°C in a nuclear reactor (1); and - supplying the heated heat exchange medium to the molecular distillation apparatus. Claim 2 In claim 1, the nuclear reactor is one of the following methods: - a gas-cooled reactor, preferably a high-temperature gas-cooled reactor or a very-high-temperature reactor, - a liquid metal-cooled reactor, - a heat pipe-cooled reactor, - a molten salt reactor. Claim 3 A method according to claim 1 or 2, wherein the evaporator (25) is operably connected to the distiller (20) and the heated heat exchange medium is supplied to the evaporator (25). Claim 4 A method comprising, in any one of claims 1 to 3, a nuclear reactor (1) comprising a reactor core (2), a primary heat exchange loop (3) including a primary heat exchange medium, wherein the primary heat exchange loop (3) passes through the reactor core (2) and passes through a primary heat exchanger (4), and a secondary heat exchange loop (12) including a secondary heat exchange medium, wherein the secondary heat exchange loop (12) passes through the primary heat exchanger (4), and transfers heat from the reactor core (2) to the secondary heat exchange medium by circulating the primary heat exchange medium in the primary heat exchange loop (3) and by circulating the secondary heat exchange medium in the secondary heat exchange loop (12). Claim 5 In paragraph 4, the secondary heat exchange loop (12) passes through the evaporator (25). Claim 6 In any one of claims 1 to 5, the distiller (20) comprises one or more of the following: - a vertical column distiller (22), - a horizontal distiller (62), - a vacuum port (29) for connecting to a vacuum system (40) for forming a high or ultra-high vacuum, - a feed port (24) for receiving a mixture of molten lithium, - a reflux port (26), - a first upper outlet port (27) for concentrated vapor lithium-6, - a second lower outlet port (28) for concentrated molten lithium-7, - a trace heating element (31), - an insulating material (32). Claim 7 A method according to any one of claims 1 to 6, wherein the evaporator (25) is operably connected to the distiller (20), and the heat exchange medium supplying heat to the evaporator (25) comprises a molten salt, preferably a nitrate, fluoride, or chloride salt having a suitable melting and boiling point. Claim 8 A method according to any one of claims 1 to 7, wherein a condenser (30) is operably coupled to the distiller (20) and includes the step of removing heat from the condenser (30) with a heat exchange medium, preferably a molten salt, preferably a nitrate, fluoride, or chloride salt. Claim 9 A method according to claim 7, wherein in claim 8, the heat exchange medium is circulated in a loop (12) comprising one or more intermediate heat exchangers (50) located between the evaporator (25) and the condenser (30), and the method comprises increasing the temperature drop between the evaporator (25) and the condenser (30), wherein the one or more intermediate heat exchangers (50) preferably comprise a counterflow recuperator (50). Claim 10 A method according to any one of claims 7 to 9, wherein the heat exchange medium preferably comprises a NaNO3-KNO3 eutectic salt having a melting point of approximately 250°C, and the evaporator (25) comprises the step of heating to at least approximately 400°C, preferably approximately 550°C. Claim 11 A method according to claim 10, comprising the step of cooling the condenser (30) to approximately 300°C, preferably to approximately 260°C. Claim 12 A method according to any one of claims 7 to 9, comprising the step of heating the evaporator (25) to approximately 400°C, preferably approximately 550°C, using a LiNO3-NaNO3-KNO3 eutectic salt having a melting point of approximately 120°C, and cooling the condenser (30) to approximately 150°C, preferably approximately 130°C. Claim 13 A method according to any one of claims 7 to 9, comprising the step of heating the evaporator (25) to approximately 600°C, preferably approximately 700°C, using a LiF-NaF-KF eutectic salt having a melting point of approximately 450°C, and cooling the condenser (30) to approximately 550°C, preferably approximately 400°C, using a LiF-NaF-KF salt or a LiNO3-NaNO3-KNO3 eutectic salt. Claim 14 A method comprising the step of heating the evaporator (25) using a LiF-NaF-KF or NaNO3-KNO3 salt and cooling the condenser (30) using an organic coolant in any one of claims 7 to 9. Claim 15 A method in which, in any one of claims 1 to 14, the distiller (20) comprises a packing (23), preferably a structured packing (23), and / or the distiller (20) is a vertical distiller (20). Claim 16 A system for isotopicly separating lithium-6 and lithium-7 from a mixture, the system comprises: a molecular distillation apparatus comprising: at least one distiller (20) configured to isotopicly separate a feed stream of molten lithium metal feed material comprising a mixture of lithium-6 and lithium-7 into a concentrated molten lithium-6 stream and a concentrated molten lithium-7 stream; an evaporator (25) operably coupled to the at least one distiller (20); a system characterized by: a nuclear reactor (1) comprising a reactor core (2); the system comprises a heat exchange arrangement for transferring heat from the nuclear reactor core (2) to the evaporator (25) using at least one heat exchange medium, the heat exchange arrangement configured to supply heat to the evaporator (25) with a heat exchange medium having a temperature of at least 400°C. Claim 17 In paragraph 16, the nuclear reactor comprises a primary heat exchange loop (3) containing a primary heat exchange medium, and the primary heat exchange loop (3) passes through the reactor core (2) and passes through the primary heat exchanger (4), and the system comprises a secondary heat exchange loop (12) containing a secondary heat exchange medium, and the secondary heat exchange loop (12) passes through the primary heat exchanger (4). Claim 18 In claim 16 or 17, the distiller (20) comprises a system including one or more of the following: - a vertical column distiller (22), - a horizontal distiller (62), - a vacuum port (29) for connecting to a vacuum system (40) for forming a high or ultra-high vacuum, - a feed port (24) for receiving a mixture of molten lithium, - a reflux port (26), - a first upper outlet port (27) for concentrated vapor lithium-6, - a second lower outlet port (28) for concentrated molten lithium-7, - a trace heating element (31), - an insulating material (32). Claim 19 A method for isotopicly separating lithium-6 and lithium-7 from a mixture, the method comprising: - isotopicly separating a molten lithium metal material comprising the mixture of lithium-6 and lithium-7 into concentrated molten lithium-6 and concentrated molten lithium-7 through molecular distillation of the molten lithium metal material using a molecular distillation apparatus comprising a distiller or a series of distillers; - heating a heat exchange medium to a temperature of at least 400°C in a nuclear reactor; and - supplying the heated heat exchange medium to the molecular distillation apparatus to drive the molecular distillation process. Claim 20 A system for isotopicly separating lithium-6 and lithium-7 from a mixture, wherein the system comprises: - a molecular distillation apparatus comprising: at least one distiller configured to isotopicly separate a molten lithium metal material comprising a mixture of lithium-6 and lithium-7 into concentrated molten lithium-6 and concentrated molten lithium-7; an evaporator operably coupled to said at least one distiller; - a nuclear reactor comprising a reactor core; wherein the system comprises a heat exchange array for transferring heat from said nuclear reactor core to said evaporator using at least one heat exchange medium, said heat exchange array configured to supply heat to said evaporator with a heat exchange medium having a temperature of at least 400°C.

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